Induction furnace



April 1931- J. v. 'BREISKY ET AL INDUCTION FURNACE Filed March 5, 1950INVENTORS M WW wu 8 aw M Y n m h J T ATTORNEY .Patented Apr. 21, 1931UNITED STATES PATENT OFFICE J'OHII V. BREISKY, OF PITTSBURGH, AND THOMASH. LONG, OF IRWIN, ."PENNSYLVANIA,

ASSIGNORS TO WESTINGHOUSE ELECTRIC AND.MANUFAOTURING COMPANY, A COR-PORATION OF PENNSYLVANIA.

INDUCTION FURNACE Application filed March 5, 1930. Serial No. 433,291.

Our invention relates to electric furnaces and, more particularly, toelectric induction furnaces.

An object of our invention is to provide means operatively associatedwith an induction furnace that shall effect deenergization of theinductor coil in case of the occurrence of certain conditions in thefurnace structure and actuate an alarm devices Another object of ourinvention is to provide a furnace construction and a control systemassociated therewith. that-will prevent molten metal, in escaping fromthe crucible and engaging the inductor coil, from destroying the coil byshort circuiting one or more turns thereof.

Another object of our invention is to provide a furnace construction anda control vent molten metal, escaping from the crucible and engaging theinductor coil, from destroying the same by simultaneously engaging aplurality of adjacent turns of the coil to short circuit the same.

Another object of our invention is to provide a ground shield in aninduction-furnace structure and means cooperating therewith and with theinductor coil for deenergizing the latter in case molten metal escapesthrough the wall of the crucible and engages the inductor coil.

In practicing our invention, we provide an inductionfurnace structureincluding a cruiten metal tr system associated therewith that will pre-'cated between the crucible and the casing and.

cible or lining, an inductor coil surrounding ing the device and systemembodying our invention.

An outer casing 11 is shown as being of pot type and is illustrative ofany casing structure for containing the other elements of the furnaceproper.

' A crucible 12, which may be of the usual kind employed in inductionfurnaces or may be in the form of a built-up lining, especially in thecase of larger furnaces, is located within the casing 11, and granularelectricinsulating material 13 is located between the crucible and thecasing.

The crucible 12 is provided with a pouring spout 14, and the casing 11may be provided with an annular cover 16 and with trunnions (not shown)to permit of tilting the furnace structure to empty the crucible 12 ofthe material which has been melted or heated therein.

An inductor coil 17 of helical shape is lomay include a plurality ofturns of a suitable electric-conducting element, here shown as beingrectangular in cross section. It may be here noted that the casing, thecrucible and the coil are illustrated in specific forms in order to showan operative combination of such elements but we desire it to beunderstood that mo'difications may be made in these elements, as they donot specifically constitute parts'of our present invention.

WVe provide a ground shield 18 of any suitable electric-conductingmaterial which is inherently of relatively high electrical resistance,and preferably non-magnetic at its normal operating temperature, whichis subdivided or of cage form in order that the heat generated thereinby eddy currents shall not be great enough to damage the adjacentinsulating material.

A member 19 of electric-insulating material, such as mica, may belocated between the coil 17 and the shield 18 .in order to obtain ahigher inherent resistance between the sl 7 and the coil than might beobtained by n e of the granular material 13, which -rconiurn it 1 areelectricalare coil 3.7.

A ground 21 is provided for supply-circuit conductor L or, more strictlyspeaking, the uppermost terminal of the coil 17 is grounded. 1

A circuit breaker 22 is connected in the circuit of the inductor coil 17and is shown schematically as connected to supply-circuit conductor L Asillustrated, the circuit breaker comprises an actuating coil 23, a core24 and cooperating stationary and movable contact members. While we haveshown aspecific form of circuit-interrupting device, we do not desire tobe limited thereto, as it may be necessary to provide a relativelylarger circuit breaker to be, in turn, controlled by a circuit breakerof the kind shown in the drawing.

, The shield 18 is grounded at 26, a currentlimiting reactor or resistor27 and the primary of a. current transformer 28- being connected inseries-circuit in the ground circuit of the shield. The terminals of thesecondary winding 29 of the current transformer are connected to theterminals of the actuating coil 23.

The circuit breaker 22 may include a second contact-bridging member andcontact members cooperating therewith to control an alarm 31, a sourceof electric energy 32 being provided to energize the alarm device 31,which may be a visual or an audible alarm and be energizedsimultaneously with the interruption of the Circuit of the inductorcoil.

- We have found that, in the melting of cer tain materials and alloys,there is a possi bility of the moltenmaterial escaping through minutecracks of fissures in the crucible to cause caking. of theelectric-insulating material 13. If there were no provision forprotecting the coil 17 against the infiltration of molten metal escapingthrough the wall of the crucible, it might be possible for such metal toengage the coil and cause a possibly fatal accident to an operatorstirring the molten metal with a metal rod, or otherwise coming intoengagement with the crucible or the molten metal.

By grounding the coil and the provision of a grounded-shield locatedbetween the coil and the crucible, we obtain an indication of dangerousconditions in the furnace structure by reason of the deenergization ofthe inductor coil and by actuation of the alarm device if and when themolten metal escaping from the crucible comes into contact with theground shield and the coil. The current-limiting reactor or resistoroperates, in the usual manner, to reduce or to limit the maximum valueof current flowing through the primary winding ofcurrent transformer 28.

It may be noted also that it is impossible to energize the inductor coil17 except momentarily if a dangerous condition as to breakdown ofinsulation between the crucible and the coil exists, or there is ameneomeo chanical breakdown or damage to the crucible itself, whichdamage is large enough to permit of the escape of moltenor othermaterial through the wall of the crucible to engage one or more of theturns of the coil.

Our system thus provides a relatively simple and highly efficient meansfor safeguarding an induction-furnace structure, including'a groundedshield, and one which effectively prevents operation of the furnace in.case of certain damage to the furnace structure and, more particularly,to the electricinsulating. material therein.

Since various vmodifications may be made inthe device and systemembodying our invention without departin from the spirit and scopethereof, we desire that only such limitations shall be placed thereon asare imposed by the prior artror are set forth in the appended claims.

We claim as our invention:

1. An induction furnace including a crucible, an inductor coil thereforand a source of electric energy for said coil, an electricconductingshield located between the crucible and the inductor coil and meansoperatively associated with the shield and'the coil for deenergizing thecoil in case escaping molten metal from said crucible engages saidshield and said coil.

2. An induction furnace including a crucible, an inductor coilsurrounding it and electric-insulating material between them, electricmeans, including an electric-conducting shield, located between the coilandthe crucible to indicate the escape of molten metal through thecrucible and to simultaneously deenergize the inductor coil.

3. An induction furnace including a crucible and an energized inductorcoil surrounding it, an extended electric-conducting shield locatedbetween the crucible and the inductor coil, :1 ground connection forsaid shield, a current transformer in said connection, and electricmeans operatively associated with the current transformer and theenergized inductor coil to indicate the engagement of the shield and thecoil by molten metal from the crucible and to efiect deenergization ofthe coil.

An induction furnace including a crucible and a surrounding energizedinductor coil, of a grounded shield between the coil and the crucible, acurrent tIfiIlSfOZlDGIflHd a reactor connected in the ground circuit ofthe shield, a ground on the inductor coil, and a circuit-interruptingmeans in the circuit of said inductor coil electrically connected to,and controlled by, said current transformer to effect deenergization ofthe inductor coil upon the shield and the coil being engaged by moltenmetal from the crucible.

5. An induction furnace including an energizing coil and a crucibletherein for containing metal to be melted, electric means, in-

rent transformer in said ground circuit hav ing a winding connected tothe circuit breaker to preclude energizationof the coil by said sourceof electric energy upon engagement of the shield and the inductor coilby material escaping from the crucible.

7. An induction furnace having a coil, a crucible therein forholding-material to be heated, a source of electric energy connected tosaid coil, a circuit breaker in the circuit of said coil, a shieldlocated between he coil and the crucible and electric-insulatingmaterial between the coil and the crucible, electric means operativelyassociated with said grounded shield for controlling the energization ofthe coil in accordance with the condition of the crucible and of theelectric-insulating material between the crucible and the coil.

8. Aninduction furnace including a crucible, an inductor coilsurrounding it and a source of electric energy for the inductor coil, anelectric-conducting shield located between the crucible and theinductorcoil and means operatively associated with the shield and the inductorcoil for indicating the simultaneous engagement of the shield and theinductor coil by metal from the crucible.

9. An induction furnace including a crucible an inductor coilsurrounding it and a source of electric energy for the inductor coil,

an electric-conducting shield located between the crucible and theinductor coil and means operatively associated with the shield and theinductor coil for indicating a breakdown of the electric insulationbetween the shield and the coil. v

10. An induction furnace including a crucible, and an inductor coiltherefor, an electric-conducting shield between the crucible and theinductor coil, electric-insulating ma= terial between the shield and thecoil and means operatively associated with the shield and the coil tocontrol the energization of the coil in accordance with the condition ofthe 1 electric-insulating material between the shield and the coil. 4

11. An induction furnace including a crucible, and an inductor coiltherefor, an electric-conducting shield and means operatively associatedwith the shield to deenergize the coil and; actuate an alarm device incase molten metal escapes from the crucible and before engages the coil.

In testimony whereof, we have hereunto subscribed our names this 26thday of February, 1930.

JOHN .V. BREISKY. THOMAS H LONG.

